Apparatus for seismic prospecting



2| o\ Buttery Receiver Amplifierfi 2 Sheets-Sheet 1 Amplifier 2 Pre- A.B. HILDEBRANDT APPARATUS FOR SEISMIC PROSPECTING Seismic Amplifier aReceiver 1 l ctcn :0 y a 600 en.

Oct. 4, 1949.

Filed Dec.

4 2 v JNVfiNTOR.

9 ,a/vzfim/ ATTO R N E Y.

Oct. 4, 1949- A. a. HILDEBRANDT 2,433,770

APPARATUS FOR SEISMIC PROSPECTING Filed Dec. 22, 1945 2 Sheets-Sheet 2F/G'.3. FIG. 4.

. 1N VEN TOR.

ATTORNEY.

Patented Oct. 4, 1949 UNITED STATES PATENT OFFICE APPARATUS FOR SEISMICPROSPECTING Alexander B. Hildebrandt, Tulsa, Okla., assignor poration ofDelaware Application December 22, 1945, Serial No. 637,054

2 Claims. 1

The present invention is directed to apparatus suitable for use inseismic exploration.

In conducting seismic operations'it is often desirable to place ageophone or. seismometer in a borehole to receive the seismic'impulses.

time required for seismic waves to travel vertically through the earth'sformation, an explosive charge will be ignited adjacent a borehole and ageophone arranged in the borehole to receive the impulse produced by theexplosive charge. Usually a series of determinations are made in theborehole using a series of explosive charges, the seismometer beingmoved along the bore of the hole to assume a diflerent position for eachexplosive charge used.

It is an object of the present invention to devise a geophone arrangedfor making a positive contact between the case of the geophone andformations penetrated by a borehole.

When employing the present invention for determining velocities, a morereliable time measurement is attained for a the first arrival of theseismic wave. The use of the present invention also enables a morereliable representation of the entire down-travelling wave group to besecured and makes for a better understanding of the seismic reflectionphenomena obtained in the area.

The above-mentioned results are believed to be obtained principally byinsuring a good contact between the seismometer case and the formationspenetrated by the borehole. In addition, the present invention enablesmeasurements to be obtained in a borehole with a slack cable between thegeophone andthe receiving and amplifying apparatus at the surface of theearth, thus eliminating the tremors which may pass down a taut cable. Itwill be understood,.however, that other advantages may be inherent inthe employment of the present invention and its operation and that I donot wish to be limited. to the abovementioned advantages or. theories. 1

Preferred embodiments of the invention, are.

shown in the drawing in which Fig. 1 shows a first embodiment arranged'for free movement in the borehole; l

Fig. 2 illustrates the embodiment of Fig. 1 with its locking device inposition to secure the geophone, to the wall of the borehole;

Fig. 3 is a fragmentary view illustrating another embodiment of thelocking device of the present invention with the, several partsin.position to allow free movement of the geophone i the borehole; and

As an example of such operations, in determining the to Standard OilDevelopment Company, a cor- Fig. 4 is a view of the embodiment of Fig. 3with the several parts of the locking device in position to engage thewall of the borehole.

Referring now specifically to the drawing and first to Fig. 1, aborehole I l penetrates the earth. Within the borehole is a geophonedesignated enerally by numeral l2 and attached to a cable l3 whichserves to suspend the geophone in the well with the upper end of thecable suspended from a hoist l4. Cable I3 is illustrated as beingconstructed with a single central conductor 15, a metal sheath l6 andinsulation I! so that the conductor l5 may serve as one branch of acircuit and the metal sheath [6 as a ground or return for the circuit. Aseismic amplifier and receiver [8 is arranged at the surface with oneterminal connected to insulated conductor l5 through connection l9 andthe other terminal connected to the metal sheath [6 by means ofconductor 20.

' to insulated conductor I5 of the cable by conductor 23 containingswitch 24.

The geophone l2 suspended by cable 13 includes a casing or shell 25 inwhich is arranged a pre-amplifler 26, a reluctance-type geophone 21 andmeans adapted to be activated by a surge of direct current sent downinsulated conductor l5 for locking the case 25 to the wall of theborehole. The construction of reluctance-type geophones andpre-amplifiers is well-known to the art and these partsof the apparatusare not shown in detail but are indicated merely by rectangles. In thedrawing, one terminal of the conductor [5 by; conductor 28 and the otherterminal. is connectedto metallic sheath ,IG v by conductor 29. Thereluctance-type geophone 21 is connectedto pre-amplifier 26 byconductors 80 and ,3l.

The means for locking the geophone l2 to the wall of ,the borehole maybe adjusted to a first position to allow the geophone to be moved freely in either directionalong the bore of the hole and maybe released toasecond position whereby the locking means secures the case 25 to thewall of the borehole. In the drawing, Fig. I

shows the locking means in the-first position to allow. the tree mo emet of e geophone alon the wall of the borehole and Fig. 2 shows thelocking means in its second position securing the case of the geophoneto the bore of the hole.

The releasable mechanism for securing the geophone against the wall ofthe borehole includes a bent lever A, a second bent lever B, spring C,shaft D, spring E and pivoted lever F. This mechanism may be arranged bythe operator at the surface of the earth to assume the first positionshown in Fig. 1 and when the device has been lowered into the boreholein the desired position, it may be released from the surface to theposition shown in Fig. 2 by a pulse of current sent down cable I3.

Openings are available in the case so that the operator at the surfaceof the earth may set the mechanism by engaging the projection 45 on arm44 with the projections 46 on each of the lever arms, as shown in Fig.1, while pressing lever F into its bottom position, making sure thatmember 5| is in the position shown inFig. 1.

The means for releasing the mechanism to the position shown in Fig. 2 isan armature 32 having its longitudinal axis vertically disposed andslidably arranged in coil of wire 33. end of the coil of wire isconnected through conductor 34, switch 35 and conductor 36 to insulatedconductor |5 of cable I 3 and the other end of the coil is connectedthrough conductor 31 to metallic cable sheath l5. Upon the closing ofswitch 24 at the surface of the earth, a direct current is sent downcable l3; the major portion of the current passes through coil 33 ratherthan the pre-amplifier 25 because the impedance of the coil is lowcompared to the impedance across the output terminals of pre-amplifier26. When the current passes through coil 33, armature 32 is drawnupwardly and strikes pivoted bar F thereby releasing the mechanism sothat it may assume the position shown in Fig. 2.

The releasable locking means will now be described in greater detail. Itwill be seen that bent lever A is made up of a short arm 40 and a longarm 4| with the lever pivoted on a horizontally extending shaft 42. Whenthe releasable locking means is in its first position, as illustrated inFig. 1, arm 4| is vertical and extends downwardly and arm 40 ishorizontal. The lower end of arm 4| is provided with a point in order toallow it to dig effectively into the wall of the borehole when themechanism is released.

The second bent lever B consists of arm 43 and arm 44 which are at rightangles with each other. The end of arm 44 is bent to form a projection45 which is parallel with arm 43 and is adapted to engage with aprojection 46 with which arm 4| of lever A is provided. Lever B ispivoted on horizontally extending pin 41. It will beseen that the upperend of spring C is secured to lever arm 40 and its lower end to leverarm 44.

Shaft D will be seen to have its axis arranged vertically and adaptedfor rotation about a journal or bearing 48 which is attached to case 25of the geophone. The end of shaft D above journal 48 is provided with aseat 49 and pivoted thereto by horizontally extending shaft 53 is arm5|. It will be seen that the arm 5| and One through an angle of bypressure applied against that face of the arm which is shown 4 in Fig. 1of the drawing, while pressure applied against any of the other faces ofthe arm cannot move arm 5| about shaft 50.

A lever 52 extending at right angles to the axis of shaft D is securedto the shaft some distance below journal 48. The upper end of spring Eis attached to that portion of case 25 forming a support for journal 48while the lower end of the spring is secured to arm 52; this arrangementof spring E exerts a bias on shaft D in the clockwise direction whenshaft D is viewed from its lower end. Attached to the lower end of shaftD is switch 35 which is arranged to complete the circuit through coil 33when the shaft is in the position shown in Fig. l and to break thecircuit when the shaft has rotated about its axis to the position shownin Fig. 2.

Jointed bar F is constructed with arms 53 and 54 secured together by a.pin or shaft 55. Arm 53 of jointed bar F is secured to lever arm 52 ofshaft D by pin 56 while arm 54 is secured to the case 25 of the geophoneby pin 51.

The mechanism may be released from the position shown in Fig. 1 to thatof Fig. 2 in the following manner. earth is closed to send a pulsethrough coil 33. The passage of the current through coil 33 drawsarmature 32 upwardly and causes it to strike the center of bar F. Asthepivot 55 of jointed bar F moves above the line joining the end pivots56 and 51-, the bar buckles under the bias exerted by spring E andallows shaft D to rotate through an angle of approximately 90. As shaftD rotates it operates switch 35 to break the electrical connectionthrough coil 33 and also rotates arm 5| through'an angle ofapproximately 90 in the clockwise direction as viewed from the lower endof the device so that the pressure exerted by spring C through lever Bon arm 5| will allow the upper arm to be bent down. As arm 5| is bentdown, lever B is rotated above pivot 41 in the clockwise manner andwithdraws projection 45 from contact with projection 46 of lever 8, thetension exerted by spring C on arm 40 of lever A then rotates lever A inthe clockwise direction about pivot 42 and the lower pointed end of arm4| is thrust against the wall of the borehole. Cable l3 may then beslackened to allow the weight of the assembly to rest on arm 4| of leverA and cause it to bite into the wall of the hole to lock the assemblyfirmly in position.

When the locking means has been released, as described above, and thegeophone case is firmly secured to the wall of the borehole, the seismicdeterminations may be obtained. It will be understood that the seismicdeterminations will be made generally in the conventional manner withthe seismic waves initiated some distance from the geophone and allowedto travel through the formations until they are received by thegeophone. Methods for initiating seismic waves and for conductingseismic operations are well known to the art and will not be describedin detail. It is to be emphasized that when the seismic waves are beingreceived by the geophone, the cable I3 is slack so that the effect ofextraneous waves which might .otherwise be transmitted down to the cableor through the fluid of the hole is reduced or eliminated. It is also tobe pointed out that the geophone assembly is securely attached to thewall of the borehole so that a tendency of the geophone assembly to failto move with the wall of the hole is reduced or eliminated.

Although the geophone is locked tightly to the Switch 24 at the surfaceof the wall of the 3 borehole by the locking means, it may be movedupwardly in the borehole by means of hoist 14 and cable 13.Determinations may be taken at any desired depth by lowering the devicein the borehole to the lowest position at which measurements are to being means, making the determination and then moving the geophoneupwardly with measurements taken at each desired point in the borehole.

Another embodiment of the present invention is shown in Figs. 3 and 4 inwhich a fragmentary view of a means for locking the geophone to the wallof the borehole is shown. It will be understood that the remainder ofthe apparatus, not shown in the drawing, may be identical with that ofFigs. land 2. The embodiment of Figs. 3 and 4 difiers from that of Figs.1 and 2 in being provided with a plurality 0f bent levers adapted forsecuring the geophone case to the wall of the hole. In the embodiment ofFigs. 3 and 4, levers A1, A: and A3 are pivoted to geophone case 25 byhorizontally extending pivot these bent levers are generally similar tobent lever A of Figs. 1 and 2, with lever arms 401, 402 and 463corresponding to arm 40 of lever A, arms 411, 412 and 413 correspondingto arm 41 of lever A and projections 461, 462 and 463 corresponding toprojection 46 of lever A. While these three levers are generally similarin appearance, they differ in that arm 412 of lever A: is shorter thanarm 411 of arm A1 and arm 413 of lever A: is shorter than arm 412. Inother words, the arms 4| 1, 412 and 413 are progressively shorter inlength.

It is usual for the diameter of boreholes to vary, due principally tothe greater erosion of the softer formations under the influence of thecirculating drilling fluid during the drilling of the well. The threearms 411, 412 and 413 are provided so that with the variations indiameter ordinarily encountered in a borehole at least one of the armswill be at a sufiiciently steep angle .to cause its end to dig into theformation and lock the geophone to the wall of the hole.

In the embodiment of Figs. 3 and 4, the levers A1, A: and A3 are securedin position with the arms 411, 412 and 413 vertical to allow thegeophone to be moved easily into and out of the hole by securing theprojections 461, 462 and 463 to projection 45' to lever B; Fig. 3 showsarms A1, A: and A: and. lever B in this relationship. It will be seenthat projection 45' and arm 44' difierfrom projection 45 and arm 44 oflever B in the embodiments of Figs. 1 and 2 in being of considerablegreater lateral extent; this lateral extension enables projection 45' toengage simultaneously with projections 461, 462 and 463 and provides aconvenient means for attaching an end of each of the springs 01. C2 andCa to lever B. It will be understood that lever B may be released in thesame manner as arm B of Figs. 1 and 2 and that upon releasing this leverarm the projection 45' is drawn upwardly by springs C1. C2 andCa andreleases simultaneously levers A1, A2 and As. Fig. 4 shows the lockingmeans with the projection 45' o! lever B disengaged from levers A1, A:and A: to release them.

taken, releasing the lock- 42. It will be seen that,

Having fully described and illustrated the present invention, what Idesire to claim is:

1. In a geophone apparatus adapted to first move freely in a boreholeand adapted subsequently to be clamped at a desired point in the hole, areleasable clamping means comprising a first lever pivoted to thegeophone apparatus, spring means associated with said first leverexerting a bias to force an end of the lever against the wall or thebore hole, a projection secured to the said first lever, a second leverpositioned to engage the projection of the first lever, spring meansassociated with said secondlever exerting a bias on the lever to causethe lever to disengage the said projection, a rotatable bar adapted tocontact said second lever to prevent disengagement in one position andto permit disengagement in a second position, a coil of wire mounted insaid geophone apparatus and an armature slideably mounted in said coiland arranged to move from a first to a second position upon the flow ofcurrent through the said coil, said armature being adapted in the saidfirst and second positions to control the rotation of the rotatable bar.

2. In a geophone apparatus for seismic prospecting, including a geophonecase adapted for vertical movement in a bore hole and for subsequentclamping at a desired point in the hole, a

releasable clamping means comprising a first lever pivotally mounted onsaid geophone case so that it is free to assume a first position inwhich one end of said lever extends downwardly and is adjacent to thegeophone case and a second position in which said lever extendsoutwardly from said geophone case in a manner adapted to force the endof said lever against the wall of the bore hole, a projection secured tosaid first lever, means biasing said first lever from its first positionto its second position, a second lever positioned to engage saidprojection on said first lever, means biasing said second lever todisengage said projection, releasing means associated'with said secondlever and adapted to assume a first position which opposes disengagementof said second lever from said projection and to assume a secondposition which permits said disengagement, and electro magnetic meansadapted to move said releasin means from its first position to itssecond position upon the flowing of an electric current through saidelectromagnetic means.

ER. B. HILDEBRANDT.

REFERENCES CITED The following reierencesare of record in the file ofthis patent:

v UNITED STATES PATENTS Number

